When you say that Criteo is already included inside your web page, do you mean Criteo's code is still included directly in your web page's source code? If so, you should remove the code from your page's source and only load the Criteo Tag through Tealium iQ. To make sure this is done properly, contact your Tealium Account Manager before removing the code.
You can find any Tag you've added to your Tealium iQ profile in the Tags tab. If you have many Tags, and finding the one you want is difficult, you can always search for it using the search bar in the upper right corner, next to the Save/Publish button. Enter "Criteo" into the search bar, and you should see a result similar to "Tags: Criteo: Criteo" from the results drop-down. Click on the result and the console will navigate to you that Tag in the Tags tab.